package com.bumptech.glide.load.model;

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.VisibleForTesting;

import com.bumptech.glide.util.LruCache;
import com.bumptech.glide.util.Util;

import java.util.Queue;

/**
 * A simple cache that can be used by {@link ModelLoader} and {@link ModelLoaderFactory} to cache
 * some data for a given model, width and height. For a loader that takes a model and returns a url,
 * the cache could be used to safely memoize url creation based on the width and height of the
 * view.
 * <p>
 * 一个可以被{@link ModelLoader}和{@link ModelLoaderFactory}通过指定模型和宽高来缓存数据的简单缓存类
 *
 * @param <A> Some Model type that implements {@link #equals} and {@link #hashCode}.
 * @param <B> Some useful type that may be expensive to create (URL, file path, etc).
 */
public class ModelCache<A, B> {
    /**
     * 默认的容量个数，而非字节数
     */
    private static final int DEFAULT_SIZE = 250;

    private final LruCache<ModelKey<A>, B> cache;

    // Public API.
    @SuppressWarnings("unused")
    public ModelCache() {
        this(DEFAULT_SIZE);
    }

    /**
     * 当存放超过指定大小时，会存放到{@link ModelKey#KEY_QUEUE}中去
     */
    public ModelCache(long size) {
        cache = new LruCache<ModelKey<A>, B>(size) {
            @Override
            protected void onItemEvicted(@NonNull ModelKey<A> key, @Nullable B item) {
                key.release();
            }
        };
    }

    /**
     * Get a value.
     *
     * @param model  The model.
     * @param width  The width in pixels of the view the image is being loaded into.
     * @param height The height in pixels of the view the image is being loaded into.
     * @return The cached result, or null.
     */
    @Nullable
    public B get(A model, int width, int height) {
        ModelKey<A> key = ModelKey.get(model, width, height);
        B result = cache.get(key);
        key.release();
        return result;
    }

    /**
     * Add a value.
     *
     * @param model  The model.
     * @param width  The width in pixels of the view the image is being loaded into.
     * @param height The height in pixels of the view the image is being loaded into.
     * @param value  The value to store.
     */
    public void put(A model, int width, int height, B value) {
        ModelKey<A> key = ModelKey.get(model, width, height);
        cache.put(key, value);
    }

    /**
     * Removes all entries from the cache.
     */
    public void clear() {
        cache.clearMemory();
    }

    @VisibleForTesting
    static final class ModelKey<A> {
        private static final Queue<ModelKey<?>> KEY_QUEUE = Util.createQueue(0);

        private int height;
        private int width;
        private A model;

        @SuppressWarnings("unchecked")
        static <A> ModelKey<A> get(A model, int width, int height) {
            ModelKey<A> modelKey;
            synchronized (KEY_QUEUE) {
                modelKey = (ModelKey<A>) KEY_QUEUE.poll();
            }
            if (modelKey == null) {
                modelKey = new ModelKey<>();
            }

            modelKey.init(model, width, height);
            return modelKey;
        }

        private ModelKey() {
        }

        private void init(A model, int width, int height) {
            this.model = model;
            this.width = width;
            this.height = height;
        }

        public void release() {
            synchronized (KEY_QUEUE) {
                KEY_QUEUE.offer(this);
            }
        }

        @Override
        public boolean equals(Object o) {
            if (o instanceof ModelKey) {
                @SuppressWarnings("unchecked") ModelKey<A> other = (ModelKey<A>) o;
                return width == other.width && height == other.height && model.equals(other.model);
            }
            return false;
        }

        @Override
        public int hashCode() {
            int result = height;
            result = 31 * result + width;
            result = 31 * result + model.hashCode();
            return result;
        }
    }
}
